The present invention relates to a process of using a thermoplastic adhesive film to laminate decorative overlays to various wood substrates. More specifically, the present invention relates to such a process wherein the thermoplastic adhesive film is non-blocking, storage stable, and can be used to laminate decorative overlays to wood substrates at temperatures of less than 250°F (121°C).

It is known in the art to utilize liquid solvent-based adhesives ("liquid adhesives") to adhere overlays to various substrates including wood substrates. However, these liquid adhesives have a number of problems or difficulties associated with them. Liquid adhesives can be difficult or messy to handle or apply, may be flammable, may present environmental concerns involving volatile organic compounds ("VOCs") and solvent recovery, or may present toxicological concerns. When used to adhere certain overlays such as thin wood veneers, liquid adhesives are known to diffuse through the overlay or"bleed through"the overlay which can destroy the visible decorative surface. This bleed through problem sometimes only becomes evident after sanding operations are performed on the visible side of the overlay. Accordingly, the bleed through problem associated with liquid adhesives can require the use of thicker, more expensive overlays.

For example, while aqueous liquid adhesives such as polyvinyl acetate and vinyl acetate-ethylene emulsions in the form of"white glue"have overcome some of the environmental and toxicity issues, these aqueous adhesives are still difficult to handle and apply, require significant drying capabilities, and require long set or cure times. They are also particularly susceptible to the bleed through problem. The water in aqueous adhesives also tends to swell wood veneer, requiring addition sanding. Adding moisture to a wood product can create problems with warpage, curl or other adverse dimensional changes.

Reactive liquid adhesives such as urea-formaldehyde ("UF"), epoxy, or urethane-based curable liquid adhesives present problems of limited shelf life or application pot stability in addition to the difficulties encountered in handling or application of the adhesives.

Because of these problems inherent in the use of liquid adhesives for bonding overlays to wood substrates, it is desirable in the industry to use thermoplastic adhesive films to bond overlays to wood substrates. One example of such a thermoplastic adhesive

film is a copolyester hot melt adhesive film (for example, Dribond available from Eastman Chemical Company). However, the present inventors have found that when copolyester films are used to laminate wood veneer to certain substrates such as Medium Density Fiberboard ("MDF") at temperatures below 250°F (121°C), the adhesion levels between the veneer and the substrate deteriorates rapidly as the lamination temperature gets farther below 250°F (121 OC). Accordingly, in applications requiring lamination temperatures below 250°F (121°C), copolyester hot melt adhesives are of little or no value.

One such example of when lower lamination temperatures are needed is the lamination of hardwood veneer to a substrate. Laminating hardwood veneer to a substrate at temperatures greater than 230°F (110°C) can undesirably cause"checking"of the hardwood veneer surface. Surface"checks"are small openings or cracks in the wood's surface (usually in flat grain surfaces). These checks develop because the wood shrinks when dried rapidly. Checking is more common in certain species of wood such as oak and beech.

Another example of a prior art adhesive film is a heat-activated and curable polyester urethane film (Bostik 812 available from Bostik). This heat activated polyester urethane film apparently can be laminated at 160-170°F (71.1-76.7°C), has excellent green strength, moisture cure and high temperature resistance. However, this film must be used with a release liner (that is, the film is not a non-blocking film) and is prohibitively expensive for many applications. This film is also not storage stable. The film comes frozen, packaged in nitrogen purged foil bags with desiccant packets and must be stored below 40°F (4.4°C).

Once the film's packaging is opened, the film must be used within 12-24 hrs, depending on ambient temperature and humidity. The overall shelf-life of the film in its original sealed bag is 90 days from manufacture if it is kept below 40°F (4.4°C).

The present invention overcomes many of the difficulties encountered by prior art methods of laminating overlays to wood substrates. In one embodiment, the present invention is a process of laminating a veneer to a wood substrate. The present invention allows for significantly better adhesion to be accomplished at much lower lamination temperatures than can be accomplished with the prior art. The improved adhesion at lower temperatures is accomplished in the present invention, utilizing an adhesive film that is also non-blocking at room temperature and storage stable.

One embodiment of the present invention is an adhesive film comprising at least one layer having a composition consisting essentially of: a) a base adhesive, said base adhesive comprising from 50 percent by weight to 100 percent by weight of said composition, said base adhesive being either an ethylene polymer having carboxylic acid functionality or an ethylene polymer capable of being modified to have carboxylic acid functionality; b) a crosslinking agent, said crosslinking agent comprising from 0 percent by weight to 50 percent by weight of said composition; c) optionally a compatibilizer; and d) optionally a curing agent.

Another embodiment of the present invention is an article comprising: a) a decorative overlay; and b) an adhesive film laminated to said overlay, said adhesive film comprising at least one layer having a composition consisting essentially of: i) a base adhesive, said base adhesive comprising from 50 percent by weight to 100 percent by weight of said composition, said base adhesive being either an ethylene polymer having carboxylic acid functionality or an ethylene polymer capable of being modified to have carboxylic acid functionality; ii) a crosslinking agent, said crosslinking agent comprising from 0 percent by weight to 50 percent by weight of said composition; iii) optionally a compatibilizer; and iv) optionally a curing agent, wherein the article is capable of being laminated to a wood substrate with glue line temperatures less than 250°F (121 °C).

Yet another embodiment of the present invention is a process of laminating a decorative overlay to a wood substrate comprising the steps of: a) placing an adhesive film between the overlay and the substrate defining a glue line, b) subjecting the overlay, adhesive film, and substrate to a sufficient amount of heat and a sufficient amount of pressure at the glue line to cause the overlay to be adhered to the substrate upon cooling to room temperature, wherein the sufficient amount of heat does not cause the temperature at the glue line to go above 250°F (121°C); and c) cooling the overlay, the adhesive film, and the substrate to a temperature sufficiently low to cause greater than 80 percent cohesive failure in the substrate upon attempted delamination of the overlay from the substrate.

Still another embodiment of the present invention is an article comprising: a) an overlay; b) a wood substrate; and c) an adhesive film positioned between said overlay and said substrate, said adhesive film laminated to said overlay and to said substrate, said adhesive film comprising at least one layer having a composition consisting essentially of: i) a base adhesive, said base adhesive comprising from 50 percent by weight to 100 percent by weight of said composition, said base adhesive being either an ethylene polymer having

carboxylic acid functionality or an ethylene polymer capable of being modified to have carboxylic acid functionality; ii) a crosslinking agent, said crosslinking agent comprising from 0 percent by weight to 50 percent by weight of said composition; iii) optionally a compatibilizer; and iv) optionally a curing agent.

Embodiments of the present invention can be advantageously utilized in end-use applications including furniture laminates, cabinet door laminates, flooring laminates, residential and architectural door skin laminates, store fixtures, high pressure laminates for countertops, veneer laminated sheet, plywood fabrication, hardboard-faced oriented strand board or plywood, and plywood forms for concrete fabrication. Additionally, rolls or sheets of adhesive backed veneer, foil polymeric film, or polymeric saturated papers can be fabricated for later thermal lamination or application to substrates.

The present invention utilizes a hot melt adhesive film. Hot melt adhesive films of the present invention comprise an ethylene polymer having carboxylic acid functionality or an ethylene polymer capable of being modified to have carboxylic acid functionality. For the purposes of this application, the phrase base adhesive will refer to such ethylene polymers having carboxylic acid functionality or an ethylene polymer capable of being modified to have carboxylic acid functionality. Hot melt adhesives of the present invention comprise from 50 percent by weight of a base adhesive to 100 percent by weight of a base adhesive.

Base adhesives useful in the present invention include copolymers of ethylene and a carboxylic acid. Preferred carboxylic acids are acrylic acid and methacrylic acid. Preferably, the amount of carboxylic acid in these carboxylic acid containing copolymers is at least 5 percent by weight of the copolymer and preferably at least 9 percent by weight of the copolymer. Ethylene-acrylic acid copolymers ("EAA") (for example, PRIMACOR resins available from The Dow Chemical Company) and ethylene-methacrylic acid ("EMAA") (for example, Nucrel resins available from DuPont) are particularly preferred base adhesives useful in the present invention. lonomerization of carboxylic acid copolymers with sodium, zinc, lithium or other inorganic salts can provide especially reactive compositions with appropriate crosslinking agents. lonomerized ethylene-carboxylic acid copolymers (for example, Surlyn resins from DuPont) have been found to be useful as base adhesives in the present invention.

Other base adhesives useful in the present invention include copolymers of ethylene and maleic anhydride or ethylene copolymers that have been grafted with or chemically

modified with maleic anhydride. Preferably, the amount of maleic anhydride in copolymers or grafts of ethylene and maleic anhydride is at least 0.5 percent by weight of the copolymer.

Other base adhesives useful in the present invention include ethylene-methyl acrylate-acrylic acid terpolymers ("EMAAA") (for example, Escor resins available from Exxon), ethylene-acrylate-maleic anhydride terpolymers based on n-butyl acrylate or ethyl acrylate (for example, Atochem Lotader resins), ethylene-vinyl acetate-grafted with maleic anhydride (for example, Fusabond available from DuPont and Orevac resins available from Atochem), and polyethylene grafted with maleic anhydride.

Still other base adhesives useful in the present invention include other olefinic and/or styrenic base adhesive polymers which are, or can be, modified with carboxylic acid functionality and/or anhydride functionality. Examples include polybutene-maleic anhydride, polybutylene-graft-maleic anhydride, polypropylene-graft-maleic anhydride, and styrenic- butadiene block copolymer-graft-maleic anhydride.

The base adhesive in the present invention can be comprised of two or more individual adhesive resins. Such a blend might be utilized in order to develop the appropriate desired base adhesive composite melt index (melt viscosity, melt strength or other physical property). A preferred embodiment of the present invention utilizes a blend of a low melt viscosity (high melt index) adhesive resin to achieve good melt flow into a porous wood substrate or wood veneer overlay with a higher melt viscosity (low melt index) adhesive resin to improve melt strength of the base adhesive blend.

The base adhesive should have a melting point less than 105°C (221 °F) and preferably less than 95°C (203°F). Additionally, base adhesive resins should have a melt index of at least 2 g/10 minutes and preferably at least 5 g/10 minutes and most preferably at least 20 g/10 minutes, when tested according to ASTM D-1238 (conditions: 190°C, 2.16 kg). Too low of adhesive melt index (too high of melt viscosity) will result in insufficient flow, wet-out and penetration into the porous wood substrate and/or the porous decorative overlay, such as wood veneer.

Preferred embodiments of the present invention utilize adhesive films containing a crosslinking agent. The crosslinking agent can be present in an amount up to 50 percent by weight of the adhesive film composition. If more than 50 percent by weight of crosslinking agent is used, the adhesive films tend to get brittle and difficult to handle. Preferably, the

amount of crosslinking agent utilized in the present invention is from 2 weight percent to 30 weight percent.

The crosslinking agent can be an epoxy resin (for example, D. E. R. or DERAKANE resins available from The Dow Chemical Company), a Novalac modified epoxy resin (for example, D. E. N. resins available from The Dow Chemical Company), or an isocyanate resin (for example, ISONATE polymeric MDI available from The Dow Chemical Company).

Preferably, crosslinking agents utilized in the present invention are epoxy resins.

These preferred crosslinking agents include epoxy resins based on diglycidyl ether of Bisphenol A. Bisphenol A advanced epoxy resins useful in the present invention will have an epoxide functionality of at least 1.8 and an epoxy equivalent weight ("EEW") of at least 170.

Epoxy resins useful in the present invention will have an EEW of no more than 6000 and preferably no more than 1800 and most preferably no more than 900.

It should be noticed by one of ordinary skill in the art that blends of base adhesives and crosslinking agents useful in the present invention are crosslinkable or curable compositions. Thus, some films of the present invention are also potentially curable.

However, it should also be noted by one of ordinary skill in the art that curing these compositions generally requires temperatures higher than 250°F (121 °C). In fact, U. S.

Patent No. 5,095,046 issued to Tse ("Tse") teaches similar compositions and states that they may form a stable molten mixture at a temperature of from 60°C (140°F) to 140°C (284°F) and may be crosslinkable by curing at a temperature of at least 150°C (302°F) for a period of time of from 10 minutes to 2 hours or more. This is in direct contrast to the present invention which advantageously provides for utilization of significantly lower lamination temperatures and significantly shorter lamination times.

Nonetheless, cured films can provide certain desirable characteristics such as higher temperature and chemical resistance, better dimensional stability, improved strength, improved abrasion resistance, and potentially a stronger cohesive bond strength. In addition, cured or crosslinked films can exhibit significantly better"green strength"or"melt strength."The phrase"green strength"and the phrase"melt strength"both refer to an adhesive's bond strength or adhesion level while still in a molten state.

This is particularly advantageous when laminating an overlay to a raised substrate, such as a patterned cabinet door. By raised substrate, it is meant that the surface of the substrate to which the overlay is to be laminated has contours and, therefore, is not flat. An

overlay laminated to a raised substrate undergoes some shaping or forming due to the contours in the raised substrate. An overlay laminated to a raised substrate is under some stress immediately after lamination because of the shaping or forming caused by the contours in the raised substrate. In such cases, an adhesive with poor green strength will permit the overlay to at least partially peel off or delaminate while the adhesive is still molten and before the laminated substrate is adequately cooled. In contrast, an adhesive with good green strength, such as the curable adhesives disclosed herein, will keep the overlay tightly bonded to the raised substrate immediately following hot pressing while the laminate cools and the adhesive solidifies.

In order to take advantage of these desirable characteristics of curable films, it may be desirable in certain embodiments of the present invention to include a curing agent or crosslinking catalyst in the composition of films of the present invention. Curing agents (or catalysts or initiators, as they may also be termed) useful in the present invention include amines, amides, amidoamine, onium halides, or boron triflourides. Especially preferred catalysts are imidazoles, such as 2-methylimidazole, and onium halides, such as tetrabutyl ammonium bromide, tetrabutyl phosphonium bromide or ethyltriphenylphosphonium acetate.

When a curing agent is incorporated into the composition of films of the present invention, it is typically present in amounts greater than 0.1 percent by weight of the film's composition and preferably at least 0.3 percent by weight. Typically, the curing agent is present in amounts no more than 1.0 percent by weight and preferably no more than 0.8 percent by weight.

Evaluation of curing kinetics, cure initiation temperature, extent of cure, and polymeric viscosity changes can be accomplished using dynamic mechanical thermal analysis. A melt rheometer, such as a Brabender Plasticorder Rheometer or a Haake Rheometer can be used to monitor rheological changes with respect to time and/or temperature. A Rheometrics RDS-2 parallel plate rheometer can be utilized with a dynamic temperature ramp to evaluate melt viscosity versus increasing temperature. A non-curing composition will typically decrease in viscosity as temperature is increased, while a curable composition will initially exhibit a viscosity reduction with increasing temperature until the cure reaction is initiated, whereupon the viscosity will increase as the temperature (or time) is increased.

In adhesive films of the present invention that utilize a crosslinking agent, it is preferred to also incorporate a compatibilizer into the composition of the film to enhance compatibility between the crosslinking agent and the base adhesive. Enhancing compatibility between the crosslinking agent and the base adhesive increases physical properties of the films such as tensile strength, elongation, and impact or puncture resistance.

When a compatibilizer is used in adhesive films of the present invention, it should be present in an amount greater than 3 percent by weight of the film composition and preferably at least 5 percent. Films of the present invention should contain no more than 50 percent of compatibilizer and preferably no more than 20 percent of compatibilizer.

Compatibilizers useful in the present invention include low-melting polyamide hot melt adhesives (for example, MACROMELT resins available from Henkel), copolymers of ethylene and vinyl acetate with at least 9 percent and preferably at least 18 percent vinyl acetate (for example, Elvax resins available from DuPont), and styrenic-olefin block copolymers (for example, Kraton resins available from Shell Chemical).

Adhesive films of the present invention can be made by conventional blown or cast extrusion, extrusion coating, hot melt roll coating, hot melt spray coating, or dispersed into a solvent and liquid coated from solution. Films of the present invention can be conventional solid films or made as an open cell foam or net web if porosity or permeability is desired, such as might be wanted to permit moisture permeation from a wood substrate.

Permeability can also be achieved by mechanical perforation of a solid film to the desired porosity. Additionally, a nonwoven adhesive web can be produced by a continuous process such as melt blown nonwoven.

Embodiments of the present invention also include multilayer films wherein one or more of the layers are made from resin compositions described herein. For example, a multilayer film could be used that has a composition of one layer tailored so as to maximize adhesion to a particular decorative overlay and a second layer having a composition tailored to maximize adhesion to a particular substrate.

Adhesive films of the present invention are typically at least 0.5 mil (12.52 microns) thick and preferably at least 1 mil (25.4 microns) thick. Adhesive films of the present invention are typically no more than 10 mils (254 microns) thick and preferably no more than 3 mils (76.2 microns) thick.

Blends of base adhesive and crosslinking agent can be compounded initially without the curing agent to form a pre-blend and then the curing agent separately added during a later film extrusion step. Alternately, a blend of base adhesive and crosslinking agent can be compounded with the curing agent at process conditions such that the curing reaction will not take place until a later process activation step (typically involving higher temperature). In a preferred process, the resins will be premelt blended in a compounding extruder with the curing agent added downstream so as to minimize temperature and residence time in the extruder and then the film directly extruded from the same extruder (that is, a compounding extruder with down stream curing agent addition directly coupled with film die and appropriate film downstream process equipment).

In a typical practice of the invention, a blend of base adhesive, crosslinking agent, and compatibilizer are melt compounded through a twin screw compounding extruder and pelletized. Separately, a masterbatch of curing agent and base adhesive is melt compounded. Both the precompound of base adhesive and crosslinking agent and the masterbatch are inherently shelf stable. The precompound and masterbatch are then melt blended at desired ratios in a film extruder and extruded into a film at a temperature typically 30-40°F (16.7-22.2°C) below the cure activation temperature of the composition. Extruding the film at a temperature below the normal curing temperature of the composition minimizes the amount of curing that takes place during extrusion. The film can later be applied at a higher temperature, causing the adhesive to cure and providing the final product with the desirable characteristics of a cured adhesive.

In another embodiment of the present invention, a base adhesive, crosslinking agent, and compatabilizer are melt compounded on a twin screw compounding extruder that has been fitted with a film die. A curing agent (in pure form or as a masterbatch) is then added downstream in the extruder. The entire mix is melt blended and extruded directly into film.

As before, the resulting film can be wound-up and stored prior to use in a particular application.

In yet another embodiment of the present invention, a base adhesive and curing agent or catalyst are melt compounded and extruded, such as through a twin screw extruder. Downstream in the extruder or just prior to the die, the crosslinking agent is added to the melt stream and intimately mixed using mixing elements on the extruder screw or through static mixers following the extruder. Adding of the crosslinking agent down stream can thus minimize reaction residence time and reduce tendency to pre-cure during extrusion.

In still another embodiment of the present invention, aqueous dispersions, emulsions or latexes of the base adhesive resin and the crosslinking agent and the curing agent can be formulated. These aqueous dispersions can then be used to liquid coat a polymeric film onto another substrate, such as a silicone coated release paper or film, or the dispersion can be saturated into a substrate, such as a kraft paper or nonwoven substrate, such as meltblown or spunbonded polypropylene or polyester nonwoven. A conventional liquid coating process, such as gravure roll coating, dip coating, meyer rod coating, doctor blade coating or liquid slot die coating, can be used to coat the liquid dispersion mixture of resins onto the carrier substrate. The coating is then dried using a forced air convection oven, or by other means, to remove the water or solvent medium and to melt fuse the resins to yield a substantially dry solid polymeric film. The use of liquid coating process can substantially reduce the thermal exposure and heat history of the reactive adhesive blend, as compared to melt extrusion.

Films of the present invention are non blocking and storage stable. By non blocking, it is meant that films of the present invention can be wound up into a roll without the use of a release liner. By storage stable, it is meant that the films can be stored at room temperature (72°F or 22.2°C, 50 percent RH) for long periods of time without spontaneously crosslinking or curing until needed in a particular application.

Adhesive films of the present invention can be used to bond two pieces of wood together or to bond a decorative overlay, vinyl, metal, fabric, plastic, cellulosic material with or without impregnated polymers, including phenolic and isocyanate saturated papers, or other material to a wood substrate or a processed wood substrate. Decorative overlays useful in the present invention include wood veneer, vinyl films, low basis weight papers, decorative foils, continuous laminates, high pressure laminates ("HPL"), cellulosic materials with or without impregnated polymeric binders (including isocyanate and phenolic saturated papers), and reconstituted wood strips. Wood substrates useful in the present invention include particleboard, medium density fiberboard ("MDF"), high density fiberboard ("HDF"), oriented strandboard ("OSB"), hardboard, hardwood plywood, veneer core plywood, isocyanate or phenolic impregnated strawboard, and wood composites made from wood fiber and polymers, such as recycled polyethylene. For purposes of this application, the definitions of types of decorative overlays and wood substrates are those that are generally known in the art. The definitions of these terms can also be found in the American National Standard hardwood and Decorative Plywood, ANSI/HPVA HP-1-1994 and Laminating Materials Association Glossary of Terms.

In a preferred embodiment of the present invention, adhesive films of the present invention are advantageously utilized to laminate wood veneer to a wood substrate. The lamination can be accomplished utilizing either a hot platen press or a membrane press.

Additionally, continuous or semi-continuous thermal lamination using a hot roll laminator or continuous belt press can be utilized to bond the overlay to the substrate. As an addition concept, the adhesive films of the present invention can be pre-laminated to one side of a decorative overlay such as a wood veneer, or a HPL facer, or to a wood substrate board. At a later time, the pre-laminated material can be further laminated onto the final substrate.

The type of wood is not critical to the workings of the present application. Typically, wood veneers used in this embodiment of the present invention are at least 0.2 mm thick.

Wood veneers used in this embodiment of the present invention are generally no more than 1.2 mm thick.

One of the advantages of using the present invention as opposed to using spray adhesives to adhere wood veneer to a wood substrate becomes even more apparent when thinner wood veneer is used. The bleed through problem associated with the use of spray adhesives worsens as thinner veneers are used. Thus, the present invention allows thinner veneer to be utilized without creating a bleed through problem.

Typically, in this embodiment of the present invention where a wood veneer or other decorative overlay, such as HPL or vinyl overlay, is laminated to a wood substrate, the adhesive film is placed between the veneer and substrate in a press and then a sufficient amount of heat and pressure is applied to cause the adhesive to melt and"wet out" (or flow into the veneer and wood substrate), bonding the veneer to the substrate. The pressure at which lamination takes place is generally greater than 20 psi (138 Kpa), and preferably greater than 50 psi (345 Kpa). Typically, the lamination pressure is no more than 300 psi (2068 Kpa), although higher pressures are possible.

In an alternative embodiment of the present invention, a prelaminated veneer or other decorative overlay is produced by laminating an adhesive film of the present invention to the veneer to produce a composite having a veneer surface and an adhesive surface.

This composite can then be stored until needed. A prelaminated veneer has improved resistance to splitting and breaking. When needed, the prelaminated veneer is placed in the press along with the substrate with the adhesive surface of the prelaminated veneer facing

the substrate. Sufficient heat and pressure are then applied to cause the adhesive to melt and"wet out", bonding the veneer to the substrate.

When laminating wood veneer or polymeric overlay, such as HPL or vinyl, to a wood substrate, it is desirable for the laminating step to be carried out at as low of a temperature as possible while still obtaining adequate adhesion of the veneer to the substrate. In fact, a particularly advantageous aspect of the present invention is that a non blocking, storage- stable-adhesive film can be utilized to laminate wood veneer to a wood substrate at glue line temperatures of less than 250°F (121°C), preferably less than 212°F (100°C), and even as low as 180°F (82. 2°C). The glue line temperature is the temperature measured at the adhesive (or"glue") layer (or"line") during lamination. This temperature is lower than the temperature at which a press would be set. The glue line temperature can be measured during lamination by attaching a thermocouple at the glue line or by placing a heat sensitive tape at the glue line.

These lower laminating temperatures are advantageous for at least the following reasons. First, laminating at lower temperatures requires less power usage in the process and can reduce cycle time between successive laminate presses. Accordingly, laminating at lower temperatures saves on processing costs and improves productivity. Second, laminating at lower temperatures causes less drying of the wood, resulting in less checking and thus a higher quality final product. Third, the present invention allows thermoplastic adhesive films to be used in certain applications requiring low lamination temperatures, where heretofore only spray adhesives have been utilized. In the case of solid, non porous decorative overlays such as HPL or polymer sheet, liquid based adhesives or moisture evaporating from the wood substrate can cause blistering of the overlay at temperatures in excess of 212°F (100°C). The use of lower temperature lamination will favorably reduce the tendency of blistering from occurring.

The adhesion levels of the decorative overlay to the wood substrate were determined by peeling back sections of overlay from the substrate, by use of a metal spatula and/or knife blade, and evaluating the peeled surface of overlay. For good adhesion, the peeled overlay should show 100 percent coverage with adhesive and particles of the wood substrate, indicating 100 percent cohesive failure in the substrate. The degree of adhesion was assessed by approximating the percent of the peeled overlay surface which was covered with wood substrate fibers or particles (that is, the percent cohesive failure of the substrate).

For example, if 50 percent of the peeled overlay surface was covered by wood particles,

then the failure was recorded as 50 percent cohesive failure in the substrate. Delamination refers to the case where 0 percent of the peeled overlay was covered by substrate, indicating failure of the adhesive bond or clean peel of the adhesive from the wood substrate.

The present invention is further illustrated by the following data and accompanying description. Nine different film compositions were tested for their ability to adhere wood veneer to a medium density fiberboard at different temperatures. The film compositions are shown in Table I. All percentage compositions are expressed as percentages based on weight of composition unless stated otherwise.

TABLE I Film Film Composition ID 1100%DRIBOND' 2 100% PRIMACOR 598012 385%PRIMACOR59801&15%D.E.R.667' 485%PRIMACOR59801,15%D.E.R.667,&0.8phrCASAMID7807 585%PRIMACOR 59801,15%D.E.R.6645,&0.8phrCASAMID780 680%PRIMACOR59801,15%D.E.R.664,5%MACROMELT62386,&0.8phr CASAMID780 780%PRIMACOR 59801,15%D.E.R.664,&5%MACROMELT6238 885%PRIMACOR 34603 &15%D.E.R.664 985%PRIMACOR3460,15%D.E.R.664,&0.8phrMACROMELT780

100% copolyester film (available from Eastman Chemical Company) 100% EAA, 20% acrylic acid, melt index = 300 g/10 min. (available from The Dow Chemical Company) 100% EAA, 9.7% acrylic acid, melt index = 20 g/10 min. (available from The Dow Chemical Company) Dow Epoxy Resin (D. E. R.), EEW = 1800, softening point = 120-135°C (available from The Dow Chemical Company) Dow Epoxy Resin, EEW = 915, softening point = 98-108°C (available from The Dow Chemical Company) 100% polyamide hot melt adhesive (available from Henkel Chemical) Blend of 83% dicyandiamide, 17% 2-methylimidazole (available from Swan Chemical)

Each of the composition blends of Films 3-9 were pre-compounded on a Werner- Pfleiderer ("WP") ZSK-30 twin screw extruder. The blend compositions were pre-mixed by tumble blending and then extruded using zone temperatures ramped from 160°F (71.1 OC) to 210°F (98.9°C) at a screw speed of 250 rpm and flow rate of 30 Ib/hr. The melt strands were cooled in a water bath and then pelletized. Following the pre-compounding, the blends were extruded on a monolayer cast film line using a 1 inch (2.54 cm) diameter Killion extruder and 10 inch (25.4 cm) wide slot die. The extruder zones were ramped from 190°F (87.8°C) to 210°F (98.9°C) with a 200°F (93.3°C) die temperature. Using a screw speed of 60 rpm, 2-3 mil films were made at 8 inch (20.32 cm) width and cooled using a 67°F (19. 4°C) casting roll. The monolayer films were wound into a roll without using a release liner.

Each of the films shown in Table I were tested for their ability to adhere red oak veneer to a Medium Density Fiberboard ("MDF"). Red oak veneer (1/42 inch thick) (. 06 cm) was cut into 2 inch (5.08 cm) by 2 inch (5.08 cm) sections and laminated to a flat MDF using a platen press. The films were placed between the veneer and MDF prior to pressure application. In each sample, 415 Kpa (60 psi) of pressure was applied for 120 seconds.

The glue line temperature was measured during lamination and recorded. After cooling to room temperature, the samples were evaluated to determine the quality of the adhesion (that is, adhesion levels) of the veneer to the MDF substrate.

The adhesion levels were determined by peeling back sections of veneer from the MDF substrate and evaluating the peeled surface of veneer. For good adhesion, the veneer should show 100 percent coverage with particles of the MDF substrate, or 100 percent cohesive failure in the substrate. The degree of adhesion was assessed by approximating the percent of the peeled veneer surface which was covered with substrate (that is, the percent cohesive failure of the MDF wood substrate). For example, if 50 percent of the peeled veneer surface was covered by wood particles, then the failure was recorded as 50 percent cohesive failure in the substrate. Delamination refers to the case where 0 percent of the peeled veneer was covered by substrate, indicating failure of the adhesive or clean peel of the adhesive from the MDF substrate.

The adhesion results are shown in Table II. These results show that the copolyester films showed considerably less adhesion capability than the other films, especially at glue line temperatures less than 250°F (121°C). The data also indicates that the EAA-based

films without curing agent (that is, without CASAMID 780) gave the best results at the lowest temperatures. This is believed to be due to the inadvertent and undesired pre-reaction or curing of these films during extrusion. Curing the films during extrusion builds the molecular weight of the adhesive, hindering the flow of the adhesive into the wood substrate or veneer.

The poorer adhesion produced by films containing PRIMACOR 3460 versus films containing PRIMACOR 59801 is due to the higher melting point of PRIMACOR 3460 (102°C melt point versus the 85°C melt point of 59801) and the higher viscosity of PRIMACOR 3460 at the lamination temperature.

TABLE II Film ID GlueLine%WoodCohesive TemperatureFailurein °F(°C)the 1 250 (i 21) 80 2 250 100 3 250 100 4 250 100 5 250 100 6 250 100 7 250 100 8 250 100 9 250 100 1 230 10 2 230 100 3 230 100 4 230 100 5 230 100 6 230 100 7 230 100 8 230 100 9 230 100 1 200 delamination 2 200 100 3 200 100 4 200 100 5 200 95 6 200 100 7 200 100 8 200 60 9 200 10 1 180 delamination 2 180 80 3 180 100 4 180 50 5 180 50 6 180 80 7 180 100 8 180 delamination 9 180 delamination

The following information, data and/or samples further illustrate aspects and embodiments of the present invention. All composition percentages are expressed as percentages by weight unless stated otherwise.

Film #10 A blend of 95 percent by weight of an ethylene-vinyl acetate-graft-maleic anhydride ("EVA-g-MAH") (Fusabond MC190 available from DuPont) (28 percent vinyl acetate, melt index = 15 g/10 min, approximately 0.8 percent maleic anhydride grafted) and 5 percent by weight of an epoxy resin (D. E. R. 661, available from The Dow Chemical Company) was melt compounded on a Werner-Pfleiderer ZSK-30 twin screw extruder at zone temperatures of 160°F (71 °C) to 210°F (99°C) and a melt temperature of 240°F (116°C). The extruded strands were water cooled and pelletized. Separately, a catalyst masterbatch was melt compounded at similar conditions on the ZSK-30 using a blend of 95 percent by weight ethylene acrylic acid (PRIMACOR 59801, available from The Dow Chemical Company) and 5 percent by weight of ethyltriphenylphosphonium acetate ("ETPPA") in methanol (30 percent by weight ETPPA and 70 percent methanol). The liquid catalyst was pumped into the extruder downstream into barrel zone 3 for incorporation into the melted EAA. This masterbatch was strand extruded, water bath cooled and pelletized. A blend of 90 percent by weight of the EVA-g-MAH and D. E. R. compound and 10 percent by weight of the ETPPA catalyst masterbatch was then extruded on a conventional slot die cast film line using extruder zone temperatures of 160°F (71 °C) to 200°F (93°C) and a die temperature of 200°F (93°C). The melt was cooled on a casting roll at 75°F (24°C) and the extrusion rate and line speed were adjusted so that a 2.5 mil (50 micron) film was produced (Film #10). The film was wound up into a film roll without using a release liner.

A laminate was produced by placing a sample of Film #10 between a 1/16 inch (. 159 cm) red oak veneer and a t/2 inch (1.27 cm) thick medium density fiberboard ("MDF") in a heated platen press at 250°F (121 OC) and 150 psi (1034 Kpa) pressure for a dwell time of 1.5 minutes. The resulting composite laminate was removed from the heated press. The oak veneer was found to be firmly adhered to the MDF and could not be easily pried off or delaminated using a spatula even when prying the still hot laminate prior to cooling. With significant force, pieces of veneer were pried off of the MDF. The removed veneer was

totally covered with MDF fibers, indicating that the adhesion of the veneer to the MDF exceeded the cohesive strength of the MDF substrate itself.

Film #11 A monolayer 2.5 mil (63 micron) film of 100 percent DuPont Fusabond MC190 (Film #11) was extruded without epoxy or catalyst using identical conditions that produced Film #10.

A laminate structure was made identical to the one used to test Film #10 above except that Film #11 was used as the adhesive. However, when the laminate using Film #11 was removed from the press, the veneer and MDF substrate could be easily pried apart with a spatula when still hot, with adhesive showing on both the veneer and the MDF substrate, indicating a cohesive failure within the hot adhesive.

Film #12 A blend of 80 percent by weight EAA (PRIMACOR 59801, available from The Dow Chemical Company) (20 percent acrylic acid, melt index = 300 g/10 min), 15 percent by weight epoxy resin (D. E. R. 661, solid, EEW = 530, Mettler softening point = 75-85°C), and 5 percent by weight ethylene vinyl acetate ("EVA") (DuPont Elvax 3180,28 percent vinyl acetate, melt index = 25 g/10 min) was melt compounded on a Werner-Pfleiderer ZSK-30 twin screw extruder at zone temperatures of 160°F (71 °C) to 210°F (99°C) and a melt temperature of 240°F (116°C). The extruded strands were water cooled and pelletized.

Separately, a catalyst masterbatch was melt compounded at similar conditions on the ZSK- 30 using a blend of 95 percent by weight EAA (PRIMACOR 59801) and 5 percent by weight tetra n-butyl ammonium bromide ("TBAB"). This masterbatch was strand extruded, water bath cooled and pelletized. A blend of 90 percent by weight of the above EAA-DER-EVA compound and 10 percent by weight of the TBAB catalyst masterbatch was then extruded on a conventional slot die cast film line using extruder zone temperatures of 160°F (71 °C) to 200°F (93°C) and die temperature of 200°F (93°F). The melt was cooled on a casting roll at 75°F (24°C) and the extrusion rate and line speed were adjusted so that a 2.5 mil film was produced (Film #12). The film was wound up into a film roll without using a release liner.

A laminate was produced identical to the laminates produced to test Film #10 and Film #11 except that Film #12 was used as the adhesive. The laminate was removed from the heated press. The veneer was found to be firmly adhered to the MDF and could not be

easily pried off or delaminated using a spatula even when prying the still hot laminate prior to cooling. However, with significant force, pieces of veneer were pried off of the MDF. The removed veneer was totally covered with MDF fibers, indicating that the adhesion of the veneer to the MDF exceeded the cohesive strength of the MDF itself.

Film #13 A blend of 70 percent by weight of EAA (PRIMACOR 59801,20 percent acrylic acid, melt index = 300 g/10 min), 25 percent by weight of epoxy resin (D. E. R. 667, EEW = 1800), and 5 percent by weight of solid phenolic curing agent (Dow Epoxy Hardener-D. E. H. 87, HEW = 385, available from The Dow Chemical Company) was melt extruded on a conventional cast film line (1 inch (25.4 mm) diameter, 24/1 UD Killion extruder with 8 inch (20.32 cm) wide slot die with 35 mil die gap, cast roll at 18°C) at 113°C to produce a 2 mil (50 micron) thick monolayer film (Film #13). The film was wound up onto itself in a roll.

Film #13 was used to adhere a High Pressure Decorative Laminate ("HPL") (manufactured by Wilsonart) to a particleboard substrate. The film was cut into 3.8 cm X 3.8 cm sections. Two of the sections were placed on top of each other and then placed on a 30 cm X 30 cm piece of particle board. Pieces of HPL 5 cm X 5 cm were placed on top of the adhesive sections. Both sides of the HPL (one side was phenolic and the other side was melamine) were tested for adhesion to the particleboard substrate. The HPL was covered with 2 sheets of Teflon to prevent sticking to the platen press. Steel plates were placed on top of the teflon and below the particleboard. All pieces were then transferred to preheated (135°C) hydraulic platen press where 200 psi (1379 Kpa) of pressure was applied for 60 seconds. After the pressure was released, the assembly was cooled for approximately 5 minutes by placing it between water cooled lower platens of the press. After cooling, the HPL pieces were removed from the particleboard substrate by prying them off with a steel scraper. Examination of the HPL pieces showed 100 percent cohesive failure in the particleboard substrate for both the phenolic and melamine sides of the HPL pieces.

Film #14 A 1.5 mil (38 micron) thick monolayer film (Film #1 4) comprised of a blend of 70 percent by weight EAA (PRIMACOR 59801), 20 percent by weight D. E. R. 667, and 10 percent by weight polyamide resin (MACROMELT 6238, available from Henkel) was made on the same cast film line used to make Film #13. Film #14 exhibited improved optical properties (better clarity, smoother surface) than that of Film #13, indicating improved

compatability of the resin blend with the addition of the polyamide. Film #14 was wound up into a film roll that was later easy to unwind.

Film #14 was cut into 3.8 cm X 3.8 cm sections and tested for adhesion between HPL and particleboard in the same manner as Film #13. Film #14 showed excellent adhesion between the HPL (both sides) and the particleboard substrate, with 100 percent cohesive failure in the particleboard substrate.

Film #15 A 2 mil (50 micron) thick monolayer film (Film #15) comprised of 80 percent by weight EAA (PRIMACOR 3460,9.7 percent acrylic acid, melt index = 20) and 20 percent by weight epoxy resin (D. E. R. 669 solid epoxy, EEW = 4500) was extruded at 280°F (140°C) to produce a tough, flexible film with good clarity. Film #15 was cut into 3.8 cm X 3.8 cm sections and tested for adhesion between HPL and particleboard in the same manner as Film #13 and Film #14, except that a pressing temperature of 149°C was used. The film showed good adhesion between the phenolic side of the HPL and particleboard substrate, with an 80 percent cohesive failure in the particleboard substrate. The film delaminated from the melamine side of the HPL.

Film #16 A two ply door skin (0.97m X 2.21 m) was fabricated using red oak veneer (0.6 mm thick) as the decorative outside surface and composite particleboard (3.2 mm thick) as the substrate. A curable adhesive film (Film #16) comprising 80 percent by weight EAA (PRIMACOR 59801), 15 percent by weight epoxy resin (D. E. R. 642), 5 percent by weight polyamide resin (MACROMELT 6238), and 0.4 phr TBAB was used as the adhesive layer between the veneer and the substrate. The thickness of the adhesive film was 3 mil (75 microns). The door skin was assembled by placing a single layer of the adhesive film between the particleboard and the veneer. The assembly was placed into a steam heated platen press and pressed at 110°C for 45 seconds at a pressure of 1038 KPa (150 psi). The door skin was removed from the press and cooled to room temperature. The integrity of the adhesive bond was tested by pulling the veneer off the particle board after cooling and determining the location of failure. The failure occurred completely within the particle board substrate, indicating that the adhesive bond was sufficient.

Film #17 A raised panel kitchen door (240 mm X 355 mm) was fabricated by laminating red oak veneer (1.2 mm thick) to a contoured particleboard substrate. A curable adhesive film (Film #17) having the same composition as Film #12 and produced in the same manner as Film #12 was used as the adhesive layer. The adhesive film was 3 mil (75 microns) thick.

The door was laminated by placing a sheet of adhesive film over the contoured particleboard and then placing a sheet of veneer on top. The assembly was placed into a Shaw-Almex membrane press and 484 KPa (70 psi) pressure was applied for 100 seconds at a membrane temperature of 150°C. The temperature at the adhesive interface (that is, the glue line) was measured using heat sensitive indicator tape to be 93°C. The pressed door was removed from the press and allowed to cool to room temperature. The integrity of the adhesive bond was tested by removing the veneer from a contoured section to determine if fibers from the particleboard substrate could be seen on the veneer. The veneer which was removed after pressing was covered with fibers from the particleboard substrate, indicating excellent adhesion between the veneer and particleboard and cohesive failure of the particleboard.

A similar test as above was perform except that Film #17 was prelaminated to the veneer prior to membrane pressing to the particleboard substrate. The prelamination was done using a Chemsultants, 18 inch (45.72 cm) wide, laboratory hot roll laminator with a setpoint of 325°F (163°C) (roll temperature of 220°F (100°C)) and a roll speed of 4 ft/min.

The film was adhered to the veneer sufficiently well so that the film could not be delaminated or peeled from the veneer without destroying the integrity of either the film or the veneer.

After pressing, the adhesion of the veneer to the substrate was evaluated in the same manner as above and showed the same result.

Film #18 A 14 mil polymeric isocyanate-saturated cellulosic paper (available from Weyerhaeuser) was thermally laminated and adhered onto oriented strand board ("OSB") using a 2.5 mil (63 micron) EAA/epoxy blend adhesive film to bond the polymeric-cellulose paper to the OSB. A blend of 60 percent PRIMACOR 59801 EAA, 20 percent PRIMACOR 3460 EAA, 15 percent Dow Epoxy Resin 642U, and 5 percent MACROMELT 6238 copolyamide was melt extruded on a twin screw compounding extruder followed by cast film extrusion using a conventional single screw extruder and slot die. The 13 mil (330 micron)

polymeric-cellulose paper, the 2.5 mil adhesive film, and the 0.5 inch (12.7 mm) thick OSB were laminated together using a conventional heated platen press at 200°F (93°C), 150 psi (1034 KPa) pressure, 2 minutes dwell time. Upon cooling, the polymeric cellulose paper could only be peeled off of the OSB with difficulty, with greater than 75 percent cohesive failure in the OSB resulting, as demonstrated by the OSB wood chips being firmly adhered to the paper and being peeled away from the OSB substrate.

Example #19 (Film #19A. B. C) Three different 2.5 mil (63 micron) thick EAA/epoxy blend films were made in a similar manner as described in the Film #12 example. A Rheometrics RDS-2 Dynamic Mechanical Spectrometer was used with 25 mm diameter parallel plate configuration to run a dynamic temperature ramp on each film. Complex viscosity with respect to temperature was monitored from 50°C to 200°C using a 10°C/minute temperature ramp rate and 1 rad/second oscillation frequency and nitrogen purge. Fifteen to twenty layers of film were stacked together on the 25 mm plates and were briefly heated to 75°C to bond the films together onto the test plates. The samples were then cooled to 50°C and the dynamic temperature ramp testing initiated.

The three films were comprised of PRIMACOR 59801 EAA, Dow Epoxy Resin 642U, Elvax 3180 EVA and tetra-n-butylammonium bromide (TBAB) cure catalyst, and had the following compositions: 19A: 100% PRIMACOR 59801 EAA 19B: 65% PRIMACOR 59801-30% D. E. R. 642U epoxy-5% Elvax 3180 EVA 19C: 65% PRIMACOR 59801-30% D. E. R. 642U epoxy-5% Elvax 3180 EVA-0.5% TBAB cure catalyst Complex Viscosity. Eta* (Pascals) Film 50°C 100°C 150°C 175°C 200°C 19A 1.1 e7 3.6 e4 3.9 e3 1.5 e3 6.4 e2 19B 1.3 e7 5.3 e4 6.3 e3 1.9 e3 7.4 e2 19C 9.6 e6 1.6 e5 1.2 e5 4.1 e5 1.4e6